1. Field of the Invention
The present invention relates to a modulator using a non-radiative dielectric waveguide, and more particularly, to a non-radiative dielectric waveguide modulator having a waveguide type hybrid coupler in which a hybrid coupler, which distributes and propagates a local oscillation signal entered from a local oscillator to a mixer of a reception unit and a modulator, is formed with conduit-shape waveguides in a conducting housing, and dielectric lines combined with the waveguides as a single body are accommodated and disposed in the conducting housing such that the structure is simplified and the manufacturing processes are reduced.
2. Description of the Related Art
Recently, research efforts have been made to implement wireless communications using transceivers in a millimeter wave band area for high speed large capacity wireless communications. As wireless communications system used in a millimeter wave band, systems mainly using waveguides had been widely used, but more recently, thanks to the semiconductor technology development, the system has been developed as a single chip called monolithic microwave integrated circuit (MMIC). The method using a waveguide, which can be referred to as a hybrid type, falls behind the MMIC in mass production and market price, but is more advantageous in small volume production.
Since a non-radiative dielectric (NRD) waveguide having less transmission loss than this method using a waveguide has been introduced first in the early 1980s, a lot of efforts to commercialize the NRD waveguide have been made and transceivers using the NRD waveguide have been actively manufactured. The NRD waveguide transfers a signal at a low loss rate through a longitudinal section magnetic (LSM) mode and by using this NRD waveguide, a circuit which provides easy compatibility with existing waveguides while maintaining the advantages of both type waveguides.
FIGS. 1a and 1b are a perspective view and a plan view, respectively, of the structure of a prior art modulator using NRD waveguides.
As shown, the prior art modulator comprises a directional coupler 10, a circulator 20, and a modulator 30. The directional coupler 10 transfers a local oscillation signal to a transmission unit and a reception unit in a transceiver, and is formed by disposing a pair of dielectric lines 12 and 14 between an upper conducting plate 40 and a lower conducting plate 50. At this time by adjusting the gap between the two dielectric lines 12 and 14, the coupling amount of the directional coupler 10 is adjusted and in order to obtain a wider bandwidth, the dielectric lines 12 and 14 should be curved as shown. A local oscillation signal generated in a local oscillator (not shown) is entered into a signal input port 12a, and this signal is propagated to the circulator 20 and a mixer port of the reception unit, respectively, by the directional coupler 10. An isolation port of this directional coupler 10 should be terminated by using a termination 16 and this termination 16 is formed by inserting a resisting sheet 16a into the dielectric line 14. Because it is very difficult to manufacture this curved dielectric line 14 and termination 16 and to obtain uniform characteristics, these are not appropriate for mass production.
The circulator 20 is a unidirectional device providing a signal path only in one direction. This circulator 20 is connected to three dielectric lines 12, 22, and 24 so that the local oscillation signal transferred from the directional coupler 10 is transferred to the modulator 30. More specifically, the local oscillation signal is input to the circulator 20 through the directional coupler 10, this signal is entered into the modulator 30 by the circulator 20, and the modulated signal reflected at the modulator 30 is output to a modulated signal output port 24a. 
This circulator 20 is formed by disposing the three dielectric lines 12, 22, and 24 at each 120° angle interval, and disposing an annular dielectric resonator 26 at the point where the three dielectric lines 12, 22, and 24 come together. Ferrite or rubber magnets are placed on the top and bottom of the annular dielectric resonator 26 and then, by using a permanent magnet, are magnetized such that the unidirectional characteristic can be obtained. In order to suppress generation of a longitudinal section electric (LSE) mode occurring in these three dielectric lines 12, 22, and 24 in addition to the LSM mode that is the basic mode, an LSE mode suppressor is inserted into the center of the dielectric lines 12, 22, and 24. Because it is difficult to manufacture the circulator 20 with the structure described above and to obtain uniform characteristics, the circulator 20 is not appropriate for mass production.
The modulator 30 comprises a Schottky diode (not shown) and by switching the local oscillation signal entered through the circulator 20 by the switching operation of the Schottky diode, modulation is performed. To this Schottky diode, a predetermined bias voltage is input and by grounding, a closed circuit is formed. That is, when the Schottky diode is on, a local oscillation signal entered into the modulator 30 is transferred to the ground and when the Schottky diode is off, is totally reflected and is output to the modulated signal output port 24a through the circulator 20, and thus amplitude shift keying (ASK) modulation is performed. A digital pulse signal that is an information signal is entered into an information signal entrance hole 32 connected to a Schottky diode mount 33, and switches the Schottky diode mounted on the Schottky diode mount 33. At this time, in order to match the Schottky diode mount 33 and a local oscillation signal, an air gap 34, a front side dielectric line 35, a high dielectric constant sheet 36, and a back side dielectric line 37 are used. Also, a patch antenna 33a of the diode mount 33 should be designed to fit the frequency of a local oscillation signal. Because the sizes of the air gap 34, the front side dielectric line 35, the high dielectric constant sheet 36, and the back side dielectric line 37 are very small, and consequently it is very difficult to manufacture these modules and to obtain uniform characteristics, these are not appropriate for mass production.
By using the principle of a parallel dielectric line coupler, a dielectric line is made to be bent and data on linewidths of dielectric lines 12 and 14 appropriate to each bend angle are established and then the directional coupler 10 as described above is designed. However, in this dielectric coupler 10, when it is desired to make a small-sized one, the bend angle cannot be reduced and if the bend is more curved, loss occurs unless the linewidths of the dielectric lines 12 and 14 should be reduced by different width with respect to angles corresponding to respective frequencies. However, it is very difficult to apply this constraint to the actual manufacturing. Also, when this directional coupler is to be mass produced, it is difficult to obtain an accurate dielectric line interval or bending angle and the isolation degree between ports is degraded. Furthermore, when in order to implement a lighter and smaller product it is desired to reduce the size further, the linewidth of the bend part should be reduced in order to increase the bending angle. However, it is difficult to accurately reduce the linewidth of the dielectric line made of Teflon and the like and therefore the actual implement is very difficult.